The present invention relates to a novel method for the preparation of a highly concentrated aqueous dispersion of a pearlescent agent used for imparting pearlescence to liquid detergents and toiletries.
It is a common practice that detergents and toiletries, such as shampoos, hair rinses, lotions, creams, soaps and the like, are imparted with pearlescence in order to improve their attractiveness and to enhance their value as commercial products. Hitherto known pearlescent agents used to impart such pearlescence are thin leaf materials of natural origin such as fish scale and mica, of which fish scale is particularly preferred.
Fish scale however, presents several problems. In addition to the low availability of high quality materials and the corresponding high cost, fish scale contains impurities which cause deterioration of and on unpleasant odor in the products formulated therewith. Therefore, fish scale is not a wholly satisfactory material for the pearlescent agent. Accordingly, as a recent trend in the industries of detergents and toiletries, fish scale is being replaced with fatty acid esters of glycols which are more readily available and capable of exhibiting pearlescence almost as good as that obtained with the pearlescent agents made from fish scale.
In order to exhibit good pearlescence, the material contained in the aqueous dispersion should be composed of very thin leafy crystals having a large light reflecting surface. With an object to control the crystal growth suitably, accordingly, crystallization of the pearlescent agent in the final product is usually carried out by precise adjustment of the formulation of the composition and the cooling velocity thereof.
Such a method of crystallization of the pearlescent agent, by in situ crystallization in the final product, has, however, limitations in the control of the crystallization conditions leading to difficulty in improving the pearlescence. Present research is, therefore, directed to the development of a new material for the pearlescent agent rather than to the improvement of the crytallization method. An alternative way has been proposed, as is disclosed in Japanese Patent Publication No. 47-804, which attempts to prepare a highly concentrated aqueous dispersion of the pearlescent agent. If an aqueous dispersion of a pearlescent agent in a concentrated form is used, manufacturing processes of many toiletry products can substantially be simplified with a possiblity of reducing the production costs.
The inventors have extensively investigated preparation of a highly concentrated aqueous dispersion of a pearlescent agent comprising a fatty acid diethanolamide and have attained a certain degree of success. The above proposed method has, however, a disadvantage of limited applications because of the necessity of a relatively large amount of the fatty acid diethanolamide.
Accordingly, there has been a strong desire to develop a novel and improved method for the preparation of a pearlescent agent, in particular, a highly concentrated aqueous dispersion thereof free from the above described problems and disadvantages of the prior art methods.